Compounds containing alkoxysilyl and polysulfide groups in the molecule are known. These compounds are utilized as interfacial binders between inorganic materials such as silica, aluminum hydroxide, talc and clay and organic materials such as thermoplastic resins, thermosetting resins and rubber, bonding agents for improving the adhesion of rubber to inorganic substrates, primers and the like.
Also known are various rubber compositions having silica loaded therein. Typical are tire tread-forming rubber compositions characterized by low heat generation and abrasion resistance. It is known in the art that compounds containing alkoxysilyl and polysulfide groups in the molecule, for example, bis-triethoxysilylpropyl tetrasulfide and bis-triethoxysilylpropyl disulfide are effective to compositions of this type. The inclusion of these compounds, however, is still insufficient to meet the requirements to further improve tensile strength, resilience and low heat generation.
One approach to improve the requisite properties is found in JP-A 2004-018511 (US Application Publication 2003/0236424 or EP 1375504A1) disclosing a compound having the average compositional formula (5):(R1O)(3-p)(R2)pSi—R3—Sm—R4—(Sn—R4)q—Sm—R3—Si(R2)p(OR1)(3-p)  (5)wherein each of R1 and R2 is a monovalent hydrocarbon group of 1 to 4 carbon atoms, each of R3 and R4 is a divalent hydrocarbon group of 1 to 15 carbon atoms, m is a positive number having an average value of 1 to 3, n is a positive number having an average value of 2 to 4, p is 0, 1 or 2, and q is 1, 2 or 3.
As disclosed therein, the organosilicon compound of the average compositional formula (5) is prepared by reacting a halogen-terminated organosilicon compound of the general formula (6):(R1O)(3-p)(R2)pSi—R3—Sm—R4—X  (6)wherein R1, R2, R3, R4, m and p are as defined above, X is a halogen atom, with an anhydrous alkali metal sulfide or anhydrous alkali metal polysulfide of the general formula (7):M2Sr  (7)wherein M is an alkali metal and r is a positive number of 1 to 4 on average, and optionally a halogen-containing compound of the general formula (8):X—R4—X  (8)wherein R4 and X are as defined above and/or sulfur.
This method, however, has some drawbacks. While it uses substantially completely anhydrous alkali metal sulfide or alkali metal polysulfide, the drying of alkali metal sulfide or alkali metal polysulfide hydrate is time consuming. Filtration of the salt is necessary. Since the method normally uses a reaction solvent, the solvent must be distilled off at the end of reaction. There remains a need for a method for the preparation of sulfide chain-bearing organosilicon compounds in a simple step and at a low cost.
For the preparation of sulfide chain-bearing organosilicon compounds, the use of phase transfer catalysts is also known. This is taught in U.S. Pat. No. 5,405,985, U.S. Pat. No. 5,468,893, U.S. Pat. No. 5,583,245, U.S. Pat. No. 6,448,426, JP-A 2004-521945 and JP-A 2004-521946. Although these patents relate to methods for preparing sulfide chain-bearing organosilicon compounds using phase transfer catalysts, no reference is made to a sulfide chain-bearing organosilicon compound having an organoxysilyl group at each end and a polysulfide group at a center of the molecule, which are linked through a monosulfide-containing divalent hydrocarbon group.